Process for the dimensionally-true sintering of ceramics

Abstract

A process for the dimensionally-true sintering of ceramic pre-shaped items, in which the firing material is resting during sintering on supporting devices, not coated with metal, which independently adapt to the shrinkage dimensions which occur during the firing process or allow a contact-free support of the pre-shaped items.

1 . A process for the dimensionally-true sintering of ceramic pre-shaped items, said process comprising: 
 resting a firing material during the sintering on supports not coated with metal or consisting of metal molten at the sinter temperature, which adapt independently to the shrinkage dimensions which occur during the firing process.    
   
   
       2 . The process according to  claim 1 , the pre-shaped items being ceramic dental prostheses.  
   
   
       3 . The process according to  claim 1 , the firing material resting on movable supporting materials which can be composed of any material which is inert vis-à-vis the firing process and does not result in adhesion to the firing material and does not contaminate the latter.  
   
   
       4 . The process according to  claim 3 , the supporting materials being developed as vertically standing or horizontally lying hollow or solid rods and having a cross-section which allows a minimal contact surface with the firing material.  
   
   
       5 . The process according to  claim 3 , the supporting materials having a tip which allows a minimal contact surface with the firing material, and being hollow or solid.  
   
   
       6 . The process according to  claim 1 , the firing material resting on supporting material which has the same physical properties as the firing material itself.  
   
   
       7 . The process according to  claim 6 , supporting material and firing material being prepared from the same preform.  
   
   
       8 . The process according to  claim 7 , the firing material being connected to a plane surface via supporting pins which are cut through after sintering.  
   
   
       9 . The process according to  claim 7 , the firing material resting in the negative mould obtained from preform through the milling process on a pourable fill material or on suitable supports and/or props.  
   
   
       10 . The process according to  claim 1  or  2 , the firing material resting on supports which has very different physical properties to the firing material itself, wherein there is no contamination or bonding of the firing material with the supports.  
   
   
       11 . The process according to  claim 1  or  2 , in which gas streams which keep the ceramic pre-shaped items floating during the sintering and are inert at the sinter temperature are used as contact-free supporting materials.  
   
   
       12 . The process according to  claim 1  or  2 , in which a magnetic field which keeps the ceramic pre-shaped items floating during the sintering because of incorporated or attached magnetic constituents is used as contact-free supporting material.  
   
   
       13 . The process according to  claim 1  or  2 , the preform containing aluminum oxide, zirconium oxide or mixed oxides of both.  
   
   
       14 . The process according to  claim 1 , wherein said movable supports contact the firing material in pre-shaped form at a contacting portion and support said firing material during sintering thereof in order to form the ceramic pre-shaped item; 
 said movable supports are operatively connected to a support structure not contacting the firing material;    and the moveable supports adapt independently to the changing dimensions of the firing material during sintering by moving with respect to the support structure without substantial movement with respect to said contacting portion of the firing material.    
   
   
       15 . The process according to  claim 14 , wherein the moveable supports are suspended hooks which support the firing material and the ceramic pre-shaped item during the sintering and said suspended hooks move towards or away from each other as the firing material changes dimensions.  
   
   
       16 . The method according  claim 14 , wherein the moveable supports are suspending hooks which move toward or away from each other during sintering of the firing material or ceramic pre-shaped material, wherein the hooks are operatively connected to rollers moveable on a track of the support structure.  
   
   
       17 . The method according  claim 16 , wherein the movable supports are operatively connected to said rollers so as to be protected by a heat insulator, and wherein said rollers are operatively connected to a mechanical, electronic and/or optical scanning device having sliding bearings which provide for force equalization during sintering.  
   
   
       18 . The method according  claim 14 , wherein the moveable supports are S-shaped suspended hooks which support the firing material and ceramic pre-shaped item during the sintering and which move towards or away from each other as the firing material or ceramic pre-shaped item changes dimensions.